Duncan Jones--too serious. Ben Stiller--not serious enough. Of those listed here, I think Verhoeven would be my first choice (though it seems like he hasn't made a movie in quite a while). Starship Troopers was packed with futuristic combat action with a heavy dollop of mordant humour. That is, in many ways, how I would describe the first Iron Man movie. He'd be prime to recapture that sensibility.

Captaindemotion wrote:

I'm not entirely convinced by this explanation, omitting, as it does, any reference to Marvel interference or the Avengers stuff. Then again, RDJ exiting Cowboys and Aliens did come as a surprise and this may explain it.

I'm not, since I have no idea why people keep getting hung-up on the Avengers stuff, insisting that a brief interlude in a feature-length film is responsible for everything they perceive to be wrong about it (and I, for one, liked Iron Man 2). I am, however, familiar with RDJr's reputation as being sometimes difficult to work with.